This invention is directed to fast curable polymers of polycyanates and polycyanate/epoxide combinations together with amine curing agents. These polymers are widely useful, specifically as laminating resins, adhesives, casting resins, underfillers, masking or encapsulating agents, coating agents. They have a high thermostability, they are fire-retardant, and their pot life and processing temperature is controllable in broad ranges.
Thermosetting materials made of polycyanates (polyfunctional cyanic acid esters of the general formula R(OCN)n) are increasingly used, specifically as laminating resins and adhesives in the high-tech area (for a review see e.g. xe2x80x9cChemistry and Technology of Cyanate Ester Resinsxe2x80x9d, I. Hamerton (ed.), Chapman and Hall, Glasgow, 1994). They are specifically characterized by high glass transition temperatures and decomposition temperatures, flame-resistance even without the addition of nonflammable additives, high viscosity compared to other thermosets having high glass transition temperatures, low dielectric losses, good adhesion to a multiplicity of substrate materials, high chemical resistance and a low corrosiveness.
The curing reaction of polycyanates (polycyclotrimerization to polycyanurates) is rather slow in case very pure monomers are used. Impurities resulting from the monomer synthesis, e.g. unreacted phenols or water, catalyze the curing reaction, but in an undefined and uncontrollable way. For this reason, very pure monomers are used, some of which are commercially available, e.g. AroCy B-10 based on Bisphenol A of Lonza AG, Schweiz. To accelerate the curing reaction and consequently to obtain more efficient methods for the manufacture of polycyanates, a variety of catalysts is used. For this purpose, especially metal acetylacetonates, zinc salts, a variety of organometallic compounds as well as phenols, and compounds containing NH radicals have successfully been used.
As known since the sixties, primary and secondary amines easily react with cyanates (see e.g. Grigat, E. et al., Angew. Chem. 79, 219 (1967)). Consequently, it has been attempted to use amines as catalysts for the cyclotrimerization of cyanates. As a result, however, the reactivity of the mixture is too high and the processing is not under control, especially when aliphatic amines arc used, e.g. common epoxide curing agents. Thus, the dicyanate AroCy(copyright) L-10 (Lonza AG) which is liquid at room temperature, abruptly turns into a gelled condition immediately as soon as a low amount of diaminohexane is admixed thereto. In contrast, by use of solid amine powder in combination with other solid catalysts (0.1-1.5 wt.-%), the formulation of a cyanate/epoxy system useful as an underfiller (U.S. Pat. No. 5,855,821) is obtained, wherein the amine is not catalytically active until an increased curing temperature is reached.
If molar amounts of an amine are used which exceed 1 mol-%, relative to the cyanate radicals, it cannot be said that the action is merely catalytic. Instead, a co-reaction between cyanate and amine occurs by which the amount of the cyanaruate structures obtained solely from the cyanates drastically decreases. This reaction has already been used for the production of curable polyaddition products (see e.g. DE 12 20 132). In this case, solutions of the amine and the cyanate were mixed, the polyadduct was separated in substance, and this mass was cured at an elevated temperature. Use of bifunctional educts yielded linear products which were linked by isourea ether groups. If trifunctional or multifunctional amines and/or trifunctional and multifunctional cyanates are solely used or used in addition, respective cross-linked plastics should be obtained.
Pre-produced polymer adducts of cyanates and amines are also useful for the production of thermoresistant thermosets, if they are mixed with other reactive resins, e.g. maleimides (U.S. Pat. Nos. 4,499,245, 4,370,467), cyclopentadienes (U.S. Pat. No. 4,469,859), polyhydantoins (U.S. Pat. No. 4,410,666), polyisocyanates (U.S. Pat. No. 4,369,302), epoxies (U.S. Pat. No. 4,393,195, EP 0,369,527) und others.
Since the presence of a larger amount of amine in a mixture of a cyanate and an amine should necessarily result in an uncontrollable production of acyclic or cross-linked polycyanates, the co-polymerization of a larger amount of an amine with a polyfunctional cyanate does not seem a possible route in order to arrive at the production of modified polycyanurates.
It is an object of the present invention to provide resin systems made of polyfunctional cyanates or mixtures of cyanates and epoxides together with amines which may be reacted to thermosetting polycyanate copolymers having a high proportion of triazine structures, as well as to provide thermosetting plastics thus obtained. Further, it is an object of the present invention to provide resin systems from which the said thermosetting polycyanates may be obtained by applying short curing times and in high reproducibility.